Complementary metal oxide semiconductor (CMOS) circuits comprise both n-type and p-type transistors, for example, n-type field effect transistors (nFETs) and p-type field effect transistors (pFETs). NFETs utilize electron carriers and pFETs utilize hole carriers. High carrier mobility is desired to provide transistors with, for example, fast switching speed. Typically, CMOS circuits are formed on silicon substrates having a (100) surface orientation. Carrier mobility, however, is affected by the surface orientation of the substrate. For example, electrons have high mobility in substrates with (100) surface orientation and holes have high mobility in substrates with (110) surface orientation. This undesirably results in the performance of pFETs being negatively impacted.
From the foregoing discussion, it is desirable to provide substrates which provide high carrier mobility for different types of carriers, such as electrons and holes.